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Synlett 2008(13): 1969-1972  
DOI: 10.1055/s-2008-1077961
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Fast and Efficient Preparation of an α-Fucosyl Building Block by Reductive 1,2-Benzylidene Ring-Opening Reaction

Daniel B. Werz*, Heiko J. Schuster, Lutz F. Tietze
Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077 Göttingen, Germany
Fax: +49(551)399476; e-Mail: dwerz@gwdg.de;
Further Information

Publication History

Received 8 May 2008
Publication Date:
15 July 2008 (online)

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Abstract

1,2-Benzylidene ring opening on fucose was promoted in the presence of different reducing agents and Lewis acids, providing a fast access to fucosyl building blocks.

Key words

carbohydrates - fucose - building block - protecting group - benzylidene

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3,4-Di- O -benzoyl-1,2- O -benzylidene-α- l -fuco-pyranose (6)
To a stirred solution of fucosyl bromide 5 (16.9 g, 31.3 mmol, 1.00 equiv) in abs. MeCN (106 mL) was added dry KI (7.46 g, 44.9 mmol, 1.43 equiv) and NaBH4 (1.13 g, 29.9 mmol, 0.96 equiv). The mixture was stirred for 2.5 h. Then more NaBH4 (1.13 g, 29.9 mmol, 0.96 equiv) was added. After a total reaction time of 5 h, the solvent was removed. The residue was dissolved in EtOAc, washed with ice water, cold sat. NaHCO3 solution, and twice with brine. The mixture was dried (Na2SO4), concentrated, and the residue purified by column chromatography (SiO2; pentane-EtOAc, 5:1) to afford 10.2 g (71%) of 6 as a colorless foam.
Analytical Data of the exo -Product
IR (KBr): 2985, 1727, 1602, 1452, 1280 cm-¹. ¹H NMR (300 MHz, CDCl3): δ = 1.31 (d, J = 6.2 Hz, 3 H), 4.51 (dd, J = 6.9, 5.2 Hz, 1 H), 4.53 (m, 1 H), 5.51 (dd, J = 6.8, 3.5 Hz, 1 H), 5.64 (dd, J = 3.4, 1.6 Hz, 1 H), 5.91 (d, J = 5.1 Hz,
1 H), 6.04 (s, 1 H), 7.31-7.65 (m, 11 H), 7.93 (m, 2 H), 8.03 (m, 2 H). ¹³C NMR (75 MHz, CDCl3): δ = 16.4, 67.8, 69.5, 71.9, 72.9, 98.8, 101.9, 126.3, 128.2, 128.6, 129.4, 129.6, 129.7, 133.2, 133.4, 137.7, 165.6, 165.7. ESI-HRMS: m/z calcd for C27H24O7Na: 483.14142; found: 483.14160.

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3,4-Di- O -benzoyl-2- O -benzyl-α/β-l-fucopyranose (7)
To a stirred solution of benzylidene fucose 6 (161 mg, 0.35 mmol, 1.0 equiv) in abs. THF (2 mL) BH3×THF (0.53 mL, 0.53 mmol, 1.5 equiv) was added at r.t., then Bu2BOTf
(52 µL, 0.053 mmol, 0.15 equiv). The mixture was stirred for 1-2 h. Water was added and the reaction mixture was extracted with EtOAc. The organic phase was dried (Na2SO4), concentrated, and the residue purified by column chromatography (SiO2; pentane-EtOAc, 3:1 to 2:1) to afford 72 mg (45%) of 7 and 70 mg (43%) of 8 as a colorless foam. The two products were easily separable (7 is much more polar than 8).
Analytical Data of the Anomeric Mixture (1:1) of 7
IR (film): 3434, 2936, 1726, 1602, 1453, 1283 cm-¹. ¹H NMR (300 MHz, CDCl3): δ = 1.19 (d, J = 6.1 Hz, 3 H), 1.27 (d, J = 6.1 Hz, 3 H), 3.38 (br s, 1 H), 3.84 (m, 2 H), 3.98 (q, J = 6.1 Hz, 1 H), 4.11 (dd, J = 7.4, 3.3 Hz, 1 H), 4.55 (q, J = 6.1 Hz, 1 H), 4.72 (d, J = 7.4 Hz, 1 H), 4.86 (d, J = 7.4 Hz, 1 H), 4.90 (m, 1 H), 5.39 (dd, J = 7.4, 3.3 Hz, 1 H), 5.43 (m, 1 H), 5.58 (m, 1 H), 5.64 (m, 1 H), 5.75 (dd, J = 7.4, 3.3 Hz, 1 H), 7.11-7.37 (m, 14 H), 7.40-7.55 (m, 6 H), 7.60 (m, 2 H), 7.81 (m, 4 H), 7.99 (m, 4 H). ¹³C NMR (75 MHz, CDCl3): δ = 16.1, 16.3, 65.1, 69.5, 70.5, 71.5, 72.3, 73.1, 73.7, 74.6, 77.4, 91.7, 97.5, 127.6, 128.0, 128.1, 128.2, 128.2, 128.3, 128.4, 128.5, 129.6, 129.7, 129.8, 129.9, 133.0, 133.0, 133.2, 133.3, 137.3, 137.8, 165.6, 165.9, 165.9. ESI-HRMS: m/z calcd for C27H26O7Na: 485.15707; found: 485.15705.

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Analytical Data of the α-Anomer
[α]D ²0 -148.4 (c 1.90, CDCl3). IR (film): 2943, 2867, 1733, 1672, 1464, 1278 cm-¹. ¹H NMR (300 MHz, CDCl3): δ = 1.24 (d, J = 6.1 Hz, 3 H), 4.29 (dd, J = 7.8, 3.4 Hz, 1 H), 4.55 (m, 1 H), 4.61 (d, J = 7.8 Hz, 1 H), 4.69 (d, J = 7.8 Hz, 1 H), 4.75-5.81 (m, 2 H), 6.68 (d, J = 3.4 Hz, 1 H), 7.23-7.33 (m, 7 H), 7.43-7.49 (m, 3 H), 7.62 (m, 1 H), 7.80 (m,
2 H), 7.94 (m, 2 H), 8.66 (s, 1 H). ¹³C NMR (75 MHz, CDCl3): δ = 16.2, 67.8, 70.3, 71.7, 72.3, 72.6, 91.2, 94.5, 127.8, 127.9, 127.9, 128.0, 128.2, 128.3, 128.5, 129.4, 129.5, 129.6, 129.7, 133.0, 133.3, 137.4, 161.4, 165.5, 165.7. ESI-HRMS: m/z calcd for C29H26Cl3NO7Na: 628.06725; found: 628.06734.